Posted
by
timothy
on Monday October 25, 2010 @04:11AM
from the ewoks-await-their-moment dept.

Luminary Crush writes "A gas giant of approximately 1.5 Mj (Jupiter Mass) was discovered on October 22nd around the binary star system HD 176051B. It's not known with certainty which component of the binary system the planet is in orbit around at this point as both stars in HD 176051B are relatively Sol-sized (1.07 and .71 solar masses). Named 176051B b, this new exoplanet orbits within the star system's habitable zone, and if mapped onto our solar system with relative distance from our Sun it would place the large planet between Earth and Mars. While it's unlikely that such a gas giant could host life as we know it (though it's hypothesized), the location of the big planet opens up the intriguing idea of the realization of some of science fiction's famously habitable moons, Pandora and Endor. Look no further than ourownsolarsystem to see moons with the potential ingredients for life — just add heat."

I am an author of the paper in which this discovery was reported. You can find a copy of the paper here [arxiv.org].

While the planet probably is near the habitable zone, this isn't the first time a giant planet has been found in the habitable zone of a star, and while it could have moons, there isn't any reason to speculate more about this planet than any of the others.

However, this planet is important for two other reasons:1. It was the first planet discovered using a technique called "astrometry", which is measuring the positions of stars in the sky, as the move up/down and left/right in reaction to a planet orbiting it. This technique has the potential to find earthlike planets in the habitable zones of nearby stars.2. It is found in a binary system and the second star is close enough that its gravity would have impacted planet formation. The leading theory of planet formation, called "core accretion", requires millions of year for planets to form, as dust in a disk around the star collides together and clings electrostatically (similar to the way dustballs collect on a hardwood floor). Eventually the dustballs grow large enough to be considered rocks, those collide and grow bigger, etc. But the second star's gravity would cause the dust to be swept out of the system in just thousands of years, far too little time for core accretion to occur. Thus, we need a different mechanism to explain planet formation in this system. This isn't the only such binary, but it this study does offer more controlled statistics of how frequently such binaries host planets, and these facts combined show that some had to form in the binary itself---the chances of a binary interacting with another star (that originally hosted the planet), leading to an exchange where the binary picks up the star, are much too small to explain the high rate observed.

Also, here [space.com] is another press story covering the discovery (by the way, stars have multiple names---don't be confused that this article calls it "HR 7162" and the other one refers to "HD 176051"---they really are the same system). The third figure on the right hand panel is particularly useful.

Check out the 3 body problem. Turns out that the only way you get long life orbit is if its orbiting just one star close enough that gravity is more or less dominated by that single object. ie to good approximation, its orbiting just one star.

For a "stable" barycenter orbit, it would have to be very far away from the stars relative to the stars own separation. IIRC even then stable orbits are problematic for the scales we are talking about.